Extending a model

I'm not sure what is the best approach for my problem. I need a model for notification (or alerts) in my application. Notifications are based on services, have multiple fields to define conditions and are associated with a user. Here's an example for a reddit notification:

user_id: 1
type: post_karma
condition: above
value: 100

And here's a weather notification:

user_id: 2
type: temperature
city: Seattle
condition: above
value: 70

So both entries are notifications but they have different condition fields. Should I:

Create different models for each type of notification?

Create a base notification model and other models for each type that extend the base one?

Only have 1 model (notification) and then some sort of condition table. A notification has multiple conditions.